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At least 19 recordsLinked to original sources

PubMed2005

Evaluation of the NIOSH MWF total particulate matter: thoracic particulate matter conversion factor in a machining environment.

Worker exposures to metalworking fluids were characterized at a plant that produced air compressors. Full-shift, side-by-side air samples (n = 147) were collected and analyzed for total particulate matter, extractable total particulate matter, thoracic particulate matter, and extractable thoracic particulate matter. The thoracic particulate matter geometric mean of 0.32 m/m (3)was below the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) of 0.4 mg/m (3). The total particulate matter geometric mean of 0.52 mg/m (3), however, was above 0.5 mg/m (3), the total particulate matter concentration offered as a surrogate REL in the NIOSHCriteria for a Recommended Standard for Occupational Exposure to Metalworking Fluids.[1]Of the 83 total particulate matter results that were at or above smash 0.5 mg/m (3), only 50 (60%) of the corresponding thoracic particulate matter results were at or above 0.4 mg/m (3). These data indicated a conversion factor of 1.65 between thoracic particulate matter and total particulate matter concentrations and 1.40 between thoracic extractable particulate matter and total extractable concentrations. These factors were significantly different from the 1.25 used to compare total particulate matter with thoracic particulate matter concentrations in the NIOSHCriteria Document[1](p < 0.01) and call into question the validity of a universal conversion factor. The authors conclude that thoracic particulate matter exposure assessment should be done directly. In terms of protecting the worker, however, the 1.25 conversion factor appeared to be conservative since each time a total particulate matter result was below 0.5 mg/m (3), its paired thoracic particulate matter measurement was below 0.4 mg/m (3).

Aluminum↗

PubMed2000

Differences between gray matter and white matter water diffusion in stroke: diffusion-tensor MR imaging in 12 patients.

PURPOSE: To investigate differences in water diffusion between white matter and gray matter in acute to early subacute stroke with diffusion-tensor magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twelve patients with unilateral middle cerebral arterial infarcts were examined with diffusion tensor-encoded echo-planar MR imaging 17 hours to 5 days after stroke onset. Isotropic diffusion coefficient (D) and diffusion anisotropy (A(sigma)) images were computed. (D) values were measured in ischemic and contralateral gray matter and white matter by using A(sigma) images to differentiate white matter from gray matter. (D) images were compared with unidirectional and directionally averaged diffusion-weighted images. RESULTS: In all patients, (D) images showed two distinct levels of diffusion reduction in the infarct; more severe reduction occurred exclusively in white matter. (D) values were significantly less in infarcted white matter than in infarcted gray matter, whereas (D) values in the contralateral white matter and gray matter were not significantly different. Relative to the contralateral side, (D) values in the infarct were reduced by 46% in white matter and by 31% in gray matter (P <.001). Diffusion-weighted imaging caused underestimation of the magnitude and, in some cases, the spatial extent of the white matter diffusion abnormality. CONCLUSION: Isotropic diffusion is more reduced in white matter than in gray matter in acute to early subacute middle cerebral arterial stroke. Diffusion-tensor imaging may be more sensitive than diffusion-weighted imaging to white matter ischemia.

Acute Disease↗

PubMed1996

Association of dementia severity with cortical gray matter and abnormal white matter volumes in dementia of the Alzheimer type.

OBJECTIVE: To examine associations between dementia severity and quantitative magnetic resonance imaging measures of cortical gray matter volume and abnormal white matter volume in 52 patients diagnosed with probable Alzheimer disease. DESIGN: Analysis of the relationship between magnetic resonance imaging volume measures and dementia severity using multiple regression and Pearson correlations. SETTING: Alzheimer's Disease Research Center, University of California, San Diego. PARTICIPANTS: Twenty-three men and 29 women with probable Alzheimer disease (average age, 71.7 years; average education, 13.3 years). MAIN OUTCOME MEASURES: The Mattis Dementia Rating Scale (MDRS) and the Mini-Mental State Examination. RESULTS: Using simultaneous multiple regression, magnetic resonance imaging volumetric measures of cortical gray matter and abnormal white matter were independently associated with dementia severity measured by either the MDRS or the Mini-Mental State Examination. Cortical gray matter volume and abnormal white matter volume also made independent contributions to performance in 4 of 5 cognitive domains assessed by the MDRS. Regional analysis indicated that limbic cortical gray matter volume and nonlimbic cortical gray matter volume were also correlated with the MDRS score; however, in the regression analysis the individual gray matter measures were not independently associated with MDRS performance. A similar analysis revealed statistically independent relationships of limbic gray matter volume and abnormal white matter volume, but not nonlimbic cortical gray matter volume, to Mini-Mental State Examination performance. CONCLUSIONS: Quantitative magnetic resonance methods provided strong evidence that cortical gray matter volume, which may reflect atrophy, and abnormal white matter volume are independently related to dementia severity in probable Alzheimer disease: lower gray matter and higher abnormal white matter volumes are associated with more severe dementia.

Aged↗

PubMed2003

Evidence of subtle gray-matter pathologic changes in healthy elderly individuals with nonspecific white-matter hyperintensities.

OBJECTIVE: To investigate whether additional "occult" tissue changes can be detected in the normal-appearing white matter and gray matter of otherwise normal elderly individuals with nonspecific white-matter hyperintensities on conventional magnetic resonance images of the brain. METHODS: Conventional and magnetization transfer magnetic resonance images were obtained from 12 otherwise normal elderly subjects with white-matter hyperintensities and 11 age- and sex-matched normal individuals. After automatic tissue segmentation, image coregistration, and masking of T2-visible lesions, we obtained magnetization transfer ratio histograms of the normal-appearing white matter and gray matter. For each histogram, the average magnetization transfer ratio, the peak height, and the peak position were measured. We also calculated the percentages of gray-matter and white-matter volumes normalized over the total volume of the intracranial content and the total normalized brain volumes. RESULTS: Average magnetization transfer ratio (P =.03) and mean peak position (P =.01) of the gray-matter histograms from elderly individuals with white-matter hyperintensities were significantly lower than the corresponding quantities from those without white-matter hyperintensities. The normalized percentages of gray and white matter and normalized brain volume did not differ between the 2 groups. The average gray-matter magnetization transfer ratio was correlated with the average lesion magnetization transfer ratio (r = 0.68; P<.01). CONCLUSIONS: This study shows that brain abnormalities in otherwise normal elderly subjects with nonspecific white-matter hyperintensities extend beyond the macroscopic white-matter lesions visualized on conventional magnetic resonance images.

Aged↗

PubMed2001

Gray matter of the bovine cervical spinal cord is mechanically more rigid and fragile than the white matter.

The gray matter of the cervical spinal cord has been thought to be equally or less rigid than the white matter. Based on this assumption, various studies have been conducted on the changes of stress distributions within the spinal cord under mechanical compression, although the mechanical properties of the white and gray matters had not been fully elucidated. The present study measured the mechanical properties of the white and gray matter of bovine spinal cords. For both the white and gray matter, the stress-strain curves had a nonlinear region, followed by a linear region, and then a region where the stresses plateaued before failure. In the nonlinear region, stress was not significantly different between the gray and white matter samples (strain approximately 0-10%), while stress and Young's modulus in the gray matter was significantly higher than the white matter in the linear part of the curve. The gray matter ruptured at lower strains than the white matter. These findings demonstrated the gray matter is more rigid and fragile than the white matter, and the conventional assumption (i.e., the white matter is more rigid than the gray matter) is not correct. We then applied our data to computer simulations using the finite element method, and confirmed that simulations agreed with actual magnetic resonance imaging findings of the spinal cord under compression. In future computer simulations, including finite element method using our data, changes in stress and strain within the cervical spinal cord under compression would be clarified in more detail, and our findings would also help to elucidate the area which can easily receive histologic damage or which could have hemodynamic disorders under mechanical compression, as well as severity and location of biochemical and molecular biological changes.

Animals↗

PubMed1982

Effects of neonatal undernutrition on the lipid composition of gray matter and white matter in rat brain.

Separate analyses were made of gray matter and white matter from rat brain after neonatal undernutrition. Newborn rats were redistributed into control, large-litter, and protein-deficient groups. Large litters had 16 rather than 8 pups with a dam. Protein-deficient dams were fed a 4%, instead of a 24%, casein diet. For controls at 21 days of age, the 2',3'-cyclic nucleotide-3'-phosphohydrolase activity was more than fivefold greater in white matter than in gray matter. Severe undernutrition (protein-deficient) gave 2',3'-cyclic nucleotide-3'-phosphohydrolase activities that were 36% lower in gray matter and 56% lower in white matter. Lipid galactose concentrations were 17% less than control in both gray matter and white matter. In protein-deficient white matter, phospholipid concentrations were 15% lower than control. Ethanolamine plasmalogens and phosphatidyl serine were affected most. Moderate nutrition (large litter) had no effect on 2',3'-cyclic nucleotide-3'-phosphohydrolase activity. A 14% deficit of galactolipids was the only difference from controls in large-litter white matter. In large-litter gray matter, phospholipid concentrations were 16% higher than controls. Nearly all glycerophospholipids, including plasmalogens, were affected. With the exception of the myelination markers, 2'3',-cyclic nucleotide-3'-phosphohydrolase and lipid galactose, the development of lipids in gray matter is almost completely spared from the effects of undernutrition. The primary effect of undernutrition is on myelination, especially in white matter.

Aging↗

PubMed1995

Automatic identification of gray matter structures from MRI to improve the segmentation of white matter lesions.

The segmentation of MRI scans of patients with white matter lesions (WML) is difficult because the MRI characteristics of WML are similar to those of gray matter. Intensity-based statistical classification techniques misclassify some WML as gray matter and some gray matter as WML. We developed a fast elastic matching algorithm that warps a reference data set containing information about the location of the gray matter into the approximate shape of the patient's brain. The region of white matter was segmented after segmenting the cortex and deep gray matter structures. The cortex was identified by using a three-dimensional, region-growing algorithm that was constrained by anatomical, intensity gradient, and tissue class parameters. White matter and WML were then segmented without interference from gray matter by using a two-class minimum-distance classifier. Analysis of double-echo spin-echo MRI scans of 16 patients with clinically determined multiple sclerosis (MS) was carried out. The segmentation of the cortex and deep gray matter structures provided anatomical context. This was found to improve the segmentation of MS lesions by allowing correct classification of the white matter region despite the overlapping tissue class distributions of gray matter and MS lesion.

Algorithms↗

PubMed2003

Microvasculature of the human cerebral white matter: arteries of the deep white matter.

The vascular architecture of the human cerebral deep white matter was studied using soft X-ray and diaphanized specimens, achieved by intra-arterial injection of barium and vascular stain respectively, and also by electron microscopic examination of the corrosion cast of arteries in normal adult brains. The deep white matter arteries passed through the cerebral cortex with a few branches to the cortex and ran straight through the white matter. The arteries concentrated ventriculopetally to the white matter around the lateral ventricle. Anastomoses were noted around the ventricular wall at the terminals of the deep white matter arteries. No centrifugal branches irrigating the periventricular white matter from the lenticulo-striate arteries were observed in the present study. The presence of anastomoses among the terminal branches of deep white matter arteries protects against ischemic change or infarction in this area from an occlusion of a single deep white matter artery. This may lead to development of terminal zone infarction from ischemia or vascular diseases, affecting multiple deep white matter arteries. The subcortical and deep white matter arteries had thick adventitial sheaths and large adventitial spaces in the white matter but not in the cortex. The presence or absence of the adventitial space is regarded as another characteristic difference between the arteries in the white matter and cortex. This difference may influence pathological changes in vascular lesions in these respective areas.

Adolescent↗

PubMed2005

White matter damage precedes that in gray matter despite similar magnetic resonance imaging changes following cerebral hypoxia-ischemia in neonatal rats.

We hypothesized that the cerebral injury produced by hypoxia-ischemia (HI) in neonatal rats would differ in white compared with gray matter as detected histologically or with magnetic resonance (MR) imaging methods. Maps of T2 and the apparent diffusion coefficient (ADC) of water were acquired in 1-week-old rats at times prior to cerebral HI (right carotid artery occlusion plus 1.5 h of hypoxia), within the last 5-10 min of HI, and 1 h or 24 h after HI. Near the end of HI, ADC decreased and T2 increased in both cortical gray and subcortical white matter within the cingulum of the HI hemisphere. One hour after HI, ADC partially recovered, but T2 remained increased and then increased further by 24 h post-HI. In contrast to the similar MR responses in white and gray matter, histological evidence for irreversible cell damage occurred in white matter earlier than in gray matter within the HI hemisphere. At 1 h post-HI, rarefied or disrupted nerve fibers and an increase in TUNEL-positive cells were observed within white matter in the cingulum, whereas neurons within the cortical gray matter appeared normal. By 24 h post-HI, damage was apparent in both white and gray matter. Thus, MR imaging detected acute tissue edema following cerebral HI in both gray and white matter but did not distinguish between the early irreversible tissue injury detected histologically in white but not gray matter in this rather severe model of neonatal encephalopathy.

Age Factors↗

PubMed1985

Computer-assisted categorization of brain computerized tomography pixels into cerebrospinal fluid, white matter, and gray matter.

A computer-assisted method was employed to estimate the amounts of cerebrospinal fluid (CSF), white matter, and gray matter in individual computerized tomography (CT) scans of brains. By means of an image processing procedure (DMORPH), the means +/- SD CT numbers of "pure" CSF, white matter, and gray matter were determined in each scan and stored. A CATSEG program used these means to define ranges for CT numbers for each of the three tissues on each scan, and to assign each pixel in a scan to one of the three categories. Summing over seven serial scans provided volumetric estimates of CSF, white matter, and gray matter in a brain segment. For 10 subjects aged 21 to 43 years, CSF volume equaled 1.4 to 4.7% of the total segment volume, white matter equaled 37.5 to 48.2%, and gray matter equaled 50.2 to 58.9%. Image processing hardware and software which allow standardized sampling from CT images for the evaluation of surface areas and CT numbers are described. These procedures, as applied to CT scans of the human brain, can be used to estimate the volumes of CSF, white matter, and gray matter in a selected intracranial segment.

Brain↗

PubMed2003

Different mechanisms of hypoxic injury on white matter and gray matter as revealed by dynamic changes in glucose metabolism in rats.

Fresh rat brain slices were incubated with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) in oxygenated Krebs-Ringer solution at 36 degrees C, and the fractional rate constant (=k3*) of [18F]FDG proportional to the cerebral glucose metabolic rate in white matter and gray matter was investigated with positron autoradiography. In both white matter and gray matter, the k3* value with > or = 20 min hypoxia was markedly lower than the unloaded control value, indicating irreversible hypoxic injury. Next, the neuroprotective effect against hypoxia induced by the addition of an N-methyl-D-aspartate receptor antagonist or a free radical scavenger was assessed by determining whether a decrease in the k3* value after hypoxia loading was prevented. In gray matter, both agents exhibited a neuroprotective effect against 20 min hypoxia. In white matter, however, only the free radical scavenger was effective. These results suggest a similarity in the degree of vulnerability to hypoxia between white matter and gray matter as well as a difference in the developmental mechanism of hypoxic injury, i.e. the involvement of both glutamate and free radicals in gray matter, and the more selective involvement of free radicals in white matter.

Animals↗

PubMed1996

Cerebral gray matter and white matter volume deficits in adolescent girls with anorexia nervosa.

OBJECTIVES: This study was undertaken to determine whether the increased cerebrospinal fluid (CSF) volumes found in anorexia nervosa (AN) are the result of differences in gray matter or white matter volumes or both. METHODS: Thirteen adolescent girls with AN who were receiving inpatient care at a tertiary-care university children's hospital and eight healthy female control subjects were studied by using magnetic resonance imaging. Images were processed by means of software developed to classify all pixels as either CSF, gray matter, or white matter. Pixels of each class were then summed across all sections. RESULTS: The AN group had larger total CSF volumes in association with deficits in both total gray matter and total white matter volumes. Lowest reported body mass index was inversely correlated with total CSF volume and positively correlated with total gray matter volume. Urinary free cortisol levels were positively correlated with total CSF volume and inversely correlated with central gray matter volume. CONCLUSIONS: These findings add support to the view that the brain abnormalities found in AN are in large part the result of the effects of the illness. The extent to which these differences in gray matter and white matter volumes are reversible with recovery remains to be established.

Adolescent↗

PubMedDate not supplied

Differentiation of gray matter and white matter perfusion in patients with unilateral internal carotid artery occlusion.

In this study, we investigated differences between gray matter and white matter perfusion in patients with a unilateral occlusion of the internal carotid artery (ICA) with dynamic susceptibility contrast. Seventeen patients and 17 control subjects were studied, using T2*-weighted gradient echo acquisition. Gray and white matter regions were obtained by segmentation of inversion recovery MRI. Lesions were excluded by segmentation of T2-weighted MRI. In the symptomatic hemisphere, cerebral blood volume was increased in white matter (P < .05) but not in gray matter. No cerebral blood flow changes were found. All timing parameters (mean transit time [MTT], time of appearance, and time to peak) showed a significant delay for both white and gray matter (P < .05), but the MTT increase of white matter was significantly larger than for gray matter (P < .05). These findings indicate that differentiation between gray and white matter is essential to determine the hemodynamic effects of an ICA occlusion.

Brain↗

PubMed2005

Relation between cerebrospinal fluid, gray matter and white matter changes in families with schizophrenia.

BACKGROUND: Gray matter reduction and ventricular enlargement belong to the best replicated findings in schizophrenia. Brain morphologic changes were also found in non-schizophrenic family members (FM). The intention of this study was to examine whether non-psychotic first-degree relatives reveal similar morphologic changes as schizophrenic patients and how state of genetic loading contribute to these abnormalities. METHODS: Forty-nine schizophrenic patients, 71 non-schizophrenic FM and 48 control subjects took part in this volumetric MRI study. All subjects were between 18 and 59 years old. Dependent variables were gray matter, white matter and total cerebrospinal fluid (CSF) volume, determined by SPM99 segmentation algorithm. As an important part of CSF lateral ventricle volume was determined manually by removing surrounding CSF areas. RESULTS: In schizophrenic patients compared to controls and non-schizophrenic FM total CSF volumes and lateral ventricles were increased. Gray and, to a lesser degree, white matter volumes were decreased as well. For CSF, gray and white matter there was no significant difference between uni- and multiple affected families. CSF correlated significantly negative with gray matter (r=-0.78) and, less intensive, with white matter (r=-0.40). There were negative correlations between gray and white matter volume as well (r=-0.26). These correlations were not significantly different between the diagnostic groups. CONCLUSION: CSF enlargement and gray matter reductions in schizophrenic patients compared to controls and non-affected FM seem to be interdependent findings. However, this correlation is independent of the factor diagnosis and is therefore not specific for schizophrenia.

Adult↗

PubMed2002

Demonstration and distribution of tau-positive glial coiled body-like structures in white matter and white matter threads in early onset Alzheimer's disease.

The present report concerns the demonstration and distribution of tau-positive structures in the frontal and temporal white matter of five autopsy cases of early onset Alzheimer's disease (AD). The relationship between white matter lesions and tau positive structures was also investigated. Five early onset AD brains, which had not only unambiguous white matter lesions, but also no or rare atherosclerosis and minimal amyloid angiopathy, were examined. There were several tau-positive coiled body-like structures and many thread-like structures in the white matter, although previous reports showed only a few coiled bodies in the white matter in the AD brain. No relationship was found between the degree of each white matter lesion and number or distribution of tau-positive structures in the white matter. The results suggest that the AD brain has tau-positive structures in the white matter similar to some neurodegenarative brain diseases such as progressive supranuclear palsy, corticobasal degeneration, and dementia with grains. However, tau abnormalities may have fewer effects when they are located in white matter lesions in AD.

Age of Onset↗

PubMed2001

Brain atrophy in relapsing-remitting multiple sclerosis: fractional volumetric analysis of gray matter and white matter.

PURPOSE: To determine the fractional brain tissue volume changes in the gray matter and white matter of patients with relapsing-remitting multiple sclerosis (MS) and to correlate these measurements with clinical disability and total lesion load. MATERIALS AND METHODS: Thirty patients with relapsing-remitting MS and 25 healthy control subjects underwent magnetic resonance imaging. Fractional brain tissue volumes (tissue volume relative to total intracranial volume) were obtained from the total segmented gray matter and white matter in each group and were analyzed. RESULTS: The fractional volume of white matter versus that of gray matter was significantly lower (-6.4%) in patients with MS (P <.0001) than in control subjects. Neither gray matter nor white matter fractional volume measurements correlated with clinical disability in the patients with MS. CONCLUSION: Loss of brain parenchymal volume in patients with relapsing-remitting MS is predominantly confined to white matter. Analysis of fractional brain tissue volumes provides additional information useful in characterizing MS and may have potential in evaluating treatment strategies.

Adult↗

PubMed2005

Plasma infusions into porcine cerebral white matter induce early edema, oxidative stress, pro-inflammatory cytokine gene expression and DNA fragmentation: implications for white matter injury with increased blood-brain-barrier permeability.

Plasma infused into porcine cerebral white matter induces both acute interstitial and delayed vasogenic edema. Edematous white matter contains extracellular plasma proteins and rapidly induces oxidative stress as evidenced by increased protein carbonyl formation and heme oxygenase-1 induction. We tested the hypothesis that edematous white matter would also upregulate pro-inflammatory cytokine gene expression and develop DNA damage. We infused autologous plasma into the frontal hemispheric white matter of pentobarbital-anesthetized pigs. We monitored and controlled physiological variables and froze brains in situ at 1, 4 or 24 hrs. We determined edema volumes by computer-assisted morphometry. We measured white matter protein carbonyl formation by immunoblotting, cytokine gene expression by standard RT-PCR methods and DNA fragmentation by agarose gel electrophoresis. White matter edema developed acutely (1 hr) after plasma infusion and increased significantly in volume between 4 and 24 hrs. Protein carbonyl formation also occurred rapidly in edematous white matter with significant elevations (3 to 4-fold) already present at 1 hr. This increase remained through 24 hrs. Pro-inflammatory cytokine gene expression was also rapidly increased at 1 hr post-infusion. Evidence for DNA fragmentation began at 2 to 4 hrs, and a pattern indicative of both ongoing necrosis and apoptosis was robust by 24 hrs. Plasma protein accumulation in white matter induces acute edema development and a cascade of patho-chemical events including oxidative stress, pro-inflammatory cytokine gene expression and DNA damage. These results suggest that in diseases with increased blood-brain barrier (BBB) permeability or following intracerebral hemorrhage or traumatic brain injury, interstitial plasma can rapidly damage white matter.

Animals↗

PubMed1995

Prenatal development of fibrous (white matter), protoplasmic (gray matter), and layer I astrocytes in the human cerebral cortex: a Golgi study.

The prenatal developmental histories of layer I, fibrous (white matter), and protoplasmic (gray matter) astrocytes have been studied in the human neocortex by the rapid Golgi method. The developmental route followed by each of these astrocytes is a distinct process which evolves from a specific precursor, occurs at a different time, and is linked to a specific event. The differentiation of layer I astrocytes is linked to the neocortex external glial limiting membrane (EGLM), that of fibrous astrocytes to the early white matter vascularization and maturation, and that of protoplasmic astrocytes to the late gray matter ascending vascularization and maturation. At the start of development, three glial precursors are established in the neocortex: 1) original radial neuroectodermal cells with nuclei above the primordial plexiform layer (PPL) by losing their ependymal and retaining their pial attachments become early astrocytes of layer I and EGLM components; 2) neuroectodermal cells with nuclei below the PPL that retain their pial and ependymal attachments become type I radial glial cells which are committed to the guidance of neurons and the early EGLM maintenance; and, 3) neuroectodermal cells that lose their pial but retain their ependymal attachment are transformed into type II radial glial precursors. By progressively losing their ependymal attachment, type II radial glia precursors become freely migrating cells, establish vascular contacts, and differentiate into fibrous astrocytes (and into oligodendrocytes?) throughout the subplate, developing white matter, and paraventricular regions. After the formation of the gray matter, additional layer I astrocytes are needed for the EGLM late prenatal and postnatal maintenance because type I radial glia cells start to regress and to reabsorb their EGLM endfeet. A late ependyma-to-pia migration of glial precursors progressively repopulates layer I with additional astrocytes and establishes the ephemeral subpial granular layer (SGL) of Ranke. From the 15th week of gestation to the time of birth, late astrocytes of layer I lose their EGLM attachments, migrate freely into the maturing gray matter, establish vascular contacts, and differentiate into protoplasmic astrocytes. The protoplasmic astrocytes of the gray matter evolve from transformation of layer I astrocytes rather than from radial glia cells as is generally believed.

Astrocytes↗